### Please describe the problem.

When importing from a directory special remote created with importtree=yes and the --json-progress option is specified, the file field is omitted from the progress objects.

### What steps will reproduce the problem?

The command

git annex import --from import-special-remote --json-progress main:Music

generates output with the file field omitted from the nested action object in the progress objects on line 2 and 4, below.

### What version of git-annex are you using? On what operating system?

10.20231228-g5540f42e21afce6947d5410c5f18b178de6c336a

on Linux

### Please provide any additional information below.

[[!format sh """
# If you can, paste a complete transcript of the problem occurring here.
# If the problem is with the git-annex assistant, paste in .git/annex/daemon.log

{\"command\":\"list\",\"error-messages\":[],\"input\":[],\"success\":true}
{\"action\":{\"command\":\"import import-special-remote\",\"input\":[]},\"byte-progress\":9972,\"percent-progress\":\"100%\",\"total-size\":9972}
{\"command\":\"import import-special-remote\",\"error-messages\":[],\"input\":[],\"success\":true}
{\"action\":{\"command\":\"import import-special-remote\",\"input\":[]},\"byte-progress\":18,\"percent-progress\":\"100%\",\"total-size\":18}
{\"command\":\"import import-special-remote\",\"error-messages\":[],\"input\":[],\"success\":true}
{\"command\":\"update\",\"error-messages\":[],\"input\":[],\"success\":true}

# End of transcript or log.
"""]]

### Have you had any luck using git-annex before? (Sometimes we get tired of reading bug reports all day and a lil' positive end note does wonders)

Yes, I am developing the easy-git-annex interface.
